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Figure 3.6
A diagram showing the sequence of events in the transformation of a
native
particle (I). As
a consequence of elevated pH and high salt concentration, the native virion in panel
A undergoes a transition to the swollen form in panel B, thereby allowing exposure
of the virion interior to proteases and ribonucleases. As proteolytic and nucleolytic
cleavage proceeds, RNA fragments, amino terminal polypeptides, and hexameric units
from the capsid are lost (C-E). Since hexamers are lost, restructuring begins (E) when
pentameric units start their 378 rotation, as they condense to the smaller particle.
In panels F-H, the pentamers continue their rotation as contraction of the assembly
proceeds simultaneously. Reproduced with permission from Larson , S. B., Lucas , R.
W., and McPherson , A. (2005) Crystallographic structure of the
T = 3
Brome mosaic virus
(BMV) virion in panel A into a
T
= 1
T
=
1
particle of brome
mosaic virus,
J. Mol. Biol.
,
346
(3), 815-831.
.. tMV
The assembly and disassembly of TMV coat proteins has been extensively
studied; reconstitution experiments yield either disk- or rod-shaped structures
as shown in Fig. 3.7 (Fraenkel-Conrat & Williams, 1955). When disassembled
and exposed to physiological conditions the coat proteins of TMV form disk
structures. The proteins aggregate into a two-layer cylindrical structure,
each layer consisting of 17 coat protein monomers (16 1/3 molecules
are present in each turn of the assembled helix). By lowering the pH and
exposure to its nucleic acid, assembly into intact virions can be initiated.
Assembly of TMV initiates at the RNA origin of assembly (OAS) site, which
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